1. Field of the Invention
This invention relates generally to drier catalysts for use in coating compositions and, more particularly, this invention relates to the use of an organic coordination complex of a manganese salt as a drier catalyst in oleoresinous coating compositions.
2. Description of the Prior Art
The use of various metal salts, such as salts of cobalt, zirconium, calcium and manganese, for example, as so-called "drier catalysts" in coating compositions is well known. Such drier catalysts promote the oxidative polymerization of the polyunsaturated oils in the composition after application in order to effect drying.
It is known that some coordination complexes of drier metals are more effective as oxidative catalysts than are the uncomplexed metal ions. For example, 1,10-phenanthroline forms coordination complexes with many metals, especially with manganese and cobalt, whereby the activity and stability or the metal is increased. See, for example, Canty et al, "1,10-Phenanthroline Promotes Drying of Paints" in Paint Industry (April 1960) and Canty et al, "1,10-Phenanthroline-Drier Catalyst Activity in Organic Coatings", Ind. & Eng. Chem., Volume 52, pages 67-70 (January 1960).
While useful, prior drier metal complexes exhibit several disadvantages. For example, 1,10 phenanthroline is quite costly, and, perhaps more importantly, is not effective in the presence of zinc oxide or zinc salts. Zinc oxide is frequently used in paints to prevent the growth of mildew, to improve color retention and, usually in conjunction with zinc chromate, zinc phosphate or zinc dust, to improve corrosion resistance.
Furthermore, 1,10-phenanthroline is a specific indicator for iron ions in concentrations as low as several ppm. At the acidic pH levels of resins and oils used in paints, 1,10-phenanthroline turns pink in the presence of a few ppm of iron and, since iron is frequently found in trace quantities in coating compositions, the use of 1,10-phenanthroline in the composition tends to turn the composition pink. This is a particular problem in water based paints, because any exposure thereof to uncoated steel will result in some pickup of iron ions from the environment.